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CONTENTS
Volume 13, Number 2, August 2017
 

Abstract
In vertical seismic isolation (VSI), a building is partitioned intentionally by vertical layers into two dynamically different substructures for seismic response reduction. Initially, a 1-story frame was partitioned into two substructures, interconnected by viscous and visco-elastic links, and seismic responses of the original and the vertically isolated structures (VIS) were obtained, considering a large number of stiffness and mass ratios of substructures with respect to the original structure. Color contour graphs were defined for presentation and investigation of large amounts of output results. Dynamic characteristics of the isolated structures were studied by considering the non-classical damping of the system, and then the effects of viscous and visco-elastic link parameters on the modal damping ratios were discussed. On this basis, three states of mass isolation, interactional state, and control mass were differentiated. Response history analyses were performed by Runge-Kutta numerical method. In these analyses, interaction of isolation ratios and link parameters, on response control of VIS was studied and the appropriate ranges for link parameters as well as the optimal ranges for isolation ratios were suggested. Results show that by using the VSI technique, seismic response reduction up to 50% in flexible substructure and even more in stiff substructure is achievable.

Key Words
vertical seismic isolation; non-classical damping; viscous and visco-elastic dampers; Runge-Kutta method; response history analyses

Address
Reza Milanchian, Masoud Nekooei: Department of Structural Engineering, Science and Research branch, Islamic Azad University, Tehran, Iran

Mahmood Hosseini: Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran


Abstract
This paper presents a numerical investigation on the seismic behavior of isolated bridges with supplemental viscous damping. Usually very large displacements make seismic isolation an unfeasible solution due to boundary conditions, especially in case of existing bridges or high risk seismic regions. First, a suggested optimal design procedure is introduced, then seismic performance of three real bridges with different isolation systems and damping levels is investigated. Each bridge is studied in four different configurations: simply supported (SSB), isolated with 10% damping (IB), isolated with 30% damping (LRB) and isolated with optimal supplemental damping ratio (IDB). Two of the case studies are investigated under spectrum compatible far-field ground motions, while the third one is subjected to near-fault strong motions. With respect to different design strategies proposed by other authors, results of the analysis demonstrated that an isolated bridge equipped with HDLRBs and a total equivalent damping ratio of 70% represents a very effective design solution. Thanks to confirmed effective performance in terms of base shear mitigation and displacement reduction under both far field and near fault ground motions, as well as for both simply supported and continuous bridges, the suggested control system provides robustness and reliability in terms of seismic performance also resulting cost effective.

Key Words
seismic response; isolated bridges; optimal design; near-fault; elastomeric bearings; supplemental damping

Address
Daniele Losano and Giorgio Serino: Department of Structures for Engineering and Architecture, University Federico II, Via Claudio 21, 80125, Naples, Italy

Houman A. Hadad: Department of Civil Architectural and Environmental Engineering, University of Miami, Florida, USA



Abstract
This paper concerns two new analytical approaches for solving high nonlinear vibration equations. Energy Balance method and Hamiltonian Approach are presented and successfully applied for nonlinear vibration equations. In these approaches, there is no need to use small parameters to solve and only with one iteration, high accurate results are reached. Numerical procedures are also presented to compare the results of analytical and numerical ones. It has been established that, the proposed approaches are in good agreement with numerical solutions.

Key Words
conservative systems; nonlinear vibration; Energy Balance method; Hamiltonian Approach

Address
M. Bayat: Young Researchers and Elite Club, Roudehen Branch, Islamic Azad University, Roudehen, Iran

I. Pakar: Young Researchers and Elites Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran

M.S. Cao: Department of Engineering Mechanics, Hohai University, Nanjing, People

Abstract
This paper focuses on the post-earthquake serviceability of steel arch bridges installed with three types of seismic dampers suffered mainshock-aftershock sequences. Two post-earthquake serviceability verification methods for the steel arch bridges are compared. The energy-absorbing properties of three types of seismic dampers, including the buckling restrained brace, the shear panel damper and the shape memory alloy damper, are investigated under major earthquakes. Repeated earthquakes are applied to the steel arch bridges to examine the influence of the aftershocks to the structures with and without dampers. The relative displacement is proposed for the horizontal transverse components in such complicated structures. Results indicate that the strain-based verification method is more conservative than the displacement-base verification method in evaluating the post-earthquake serviceability of structures and the seismic performance of the retrofitted structure is significantly improved.

Key Words
post-earthquake serviceability; seismic damper; steel arch bridge; displacement-based verification method; strain-based verification method; seismic performance

Address
Ran Li: School of Civil Engineering, Southeast University, 2 Sipailou, Xuanwu District, Nanjing, 210096, China
(Former Visiting Scholar, Meijo University, Nagoya, Japan)

Hanbin Ge and Rikuya Maruyama: Department of Civil Engineering, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 464-8502, Japan


Abstract
This article aims to investigate the possible retrofitting of a deficient building with soft story failure mode by connecting it to an adjacent building which is designed based on current code with friction dampers at all floors. Low cost and high performance reliability along with significant energy dissipation pertaining to stable hysteretic loops may be considered in order to choose the proper damper for connecting adjacent buildings. After connecting two neighbouring floors by friction dampers, the sliding forces of dampers at various stories are set in two arrangements: uniform sliding force and then variable sliding force. In order to account for the stochastic nature of the seismic events, incremental dynamic analyses are employed prior and after the installation of the friction dampers at the various floors. Based on these results, fragility curves and mean annual rate of exceedance of serviceability and ultimate limit states are obtained. The results of this study show that the collapse mode of the deficient building can affect the optimum arrangement of sliding forces of friction dampers at Collapse Prevention (CP) performance level. In particular, the Immediate Occupancy (IO) performance level is not tangible to the sliding force arrangement and it depends solely on sliding force value. Generally it can be claimed that this rehabilitation scheme can turn the challenge of pounding two adjacent buildings into the opportunity of dissipating a large amount of the seismic input energy by the friction dampers, thus improving significantly the poor seismic performance of the deficient structure.

Key Words
coupled buildings; friction damper; incremental dynamic analysis; fragility curve; mean annual frequency

Address
Seyed Bahram Beheshti Aval, Amir Farrokhi and Ahmad Fallah: Department of Structural Engineering, Faculty of Civil Engineering,
K.N. Toosi University of Technology, No. 1346, Vali Asr Street, Mirdamad Intersection, Tehran, Iran

Apostolos Tsouvalas: Department of Structural Engineering, Faculty of Civil Engineering and Geosciences,
Delft University of Technology, building 23, Delft, Netherlands


Abstract
Multi-Axial Testing System (MATS) is a 6-DOF loading system located at National Center for Research on Earthquake Engineering (NCREE) in Taiwan for advanced seismic testing of structural components or sub-assemblages. MATS was designed and constructed for a large variety of structural testing, especially for the specimens that require to be subjected to vertical and longitudinal loading simultaneously, such as reinforced concrete columns and lead rubber bearings. Functionally, MATS consists of a high strength self-reacting frame, a rigid platen, and a large number of servo-hydraulic actuators. The high strength self-reacting frame is composed of two post-tensioned A-shape reinforced concrete frames interconnected by a steel-and-concrete composite cross beam and a reinforced concrete reacting base. The specimen can be anchored between the top cross beam and the bottom rigid platen within a 5-meter high and 3.25-meter wide clear space. In addition to the longitudinal horizontal actuators that can be installed for various configurations, a total number of 13 servo-hydraulic actuators are connected to the rigid platen. Degree-of-freedom control of the rigid platen can be achieved by driving these actuators commanded by a digital controller. The specification and information of MATS in detail are described in this paper, providing the users with a technical point of view on the design, application, and limitation of MATS. Finally, future potential application employing advanced experimental technology is also presented in this paper.

Key Words
multi-axial testing system; degree-of-freedom control; advanced experimental technology; structural testing

Address
Te-Hung Lin and Ker-Chun Lin: National Center for Research on Earthquake Engineering, National Applied Research Laboratories,
200, Sec. 3, HsinHai Rd., Taipei 106, Taiwan

Pei-Ching Chen: Department of Civil and Construction Engineering, National Taiwan University of Science and Technology,
No.43, Keelung Rd., Sec.4, Taipei 106, Taiwan


Abstract
In the present study, exterior beam column sub-assemblages are designed in accordance with the codal stipulations prevailed at different times prior to the introduction of modern seismic provisions, viz., i) Gravity load designed with straight bar anchorage (SP1), ii) Gravity load designed with compression anchorage (SP1-D), iii) designed for seismic load but not detailed for ductility (SP2), and iv) designed for seismic load and detailed for ductility (SP3). Comparative seismic performance of these exterior beam-column sub-assemblages are evaluated through experimental investigations carried out under repeated reverse cyclic loading. Seismic performance parameters like load-displacement hysteresis behavior, energy dissipation, strength and stiffness degradation, and joint shear deformation of the specimens are evaluated. It is found from the experimental studies that with the evolution of the design methods, from gravity load designed to non-ductile and then to ductile detailed specimens, a marked improvement in damage resilience is observed. The gravity load designed specimens SP1 and SP1-D respectively dissipated only one-tenth and one-sixth of the energy dissipated by SP3. The specimen SP3 showcased tremendous improvement in the energy dissipation capacity of nearly 2.56 times that of SP2. Irrespective of the level of design and detailing, energy dissipation is finally manifested through the damage in the joint region. The present study underlines the seismic deficiency of beam-column sub-assemblages of different design evolutions and highlights the need for their strengthening/retrofit to make them fit for seismic event.

Key Words
beam-column sub-assemblage; seismic design; ductile detailing; energy dissipation; strength degradation; shear deformation

Address
A. Kanchana Devi and K. Ramanjaneyulu: CSIR-Structural Engineering Research Centre, Chennai, 600113, Tamil Nadu, India

A. Kanchana Devi and K. Ramanjaneyulu: Academy of Scientific and Innovative Research (AcSIR), Chennai, 600113, Tamil Nadu, India



Abstract
To overcome the difficulty of performing multi-point response spectrum analysis for engineering structures under spatially varying ground motions (SVGM) using the general finite element code such as ANSYS, an approach has been developed by improving the modelling of the input ground motions in the spectral analysis. Based on the stochastic vibration analyses, the cross-power spectral density (c-PSD) matrix is adopted to model the stationary SVGM. The design response spectra are converted into the corresponding PSD model with appropriate coherency functions and apparent wave velocities. Then elements of c-PSD matrix are summarized in the row and the PSD matrix is transformed into the response spectra for a general spectral analysis. A long-span high-pier bridge under multiple support excitations is analyzed using the proposed approach considering the incoherence, wave-passage and site-response effects. The proposed approach is deemed to be an efficient numerical method that can be used for seismic analysis of large engineering structures under SVGM.

Key Words
response spectral analysis; multiple support excitation; stochastic vibration analysis; high-pier railway bridge; seismic spatial variability

Address
Lanping Li, Yizhi bu, Hongyu Jia, Shixiong Zheng and Deyi Zhang: Department of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China

Hongyu Jia: The Key Laboratory of Urban Security and Disaster Engineering, Beijing University of Technology, Beijing 100124, China

Kaiming Bi: Center for Infrastructure Monitoring and Protection, School of Civil Engineering and Mechanics,
Curtin University, Kent St, Bentley, WA 6102, Australia


Abstract
This work aims to analyze the thermo-viscoelastic interaction in an orthotropic solid cylinder. The medium is considered to be variable thermal conductivity and subjected to temperature pulse. Analytical solution based on dual-phase-lags model with Voigt-type for behavior of viscoelastic material has been effectively proposed. All variables are deduced using method of Laplace transforms. Numerical results for different distribution fields, such as temperature, displacement and stress components are graphically presented. Results are discussed to illustrate the effect of variability thermal conductivity parameter as well as phase-lags and viscoelasticity on the field quantities. Results are obtained when the viscosity is ignored with and without considering variability of thermal conductivity. A comparison study is made and all results are investigated.

Key Words
thermoviscelasticity; orthotropic medium; solid cylinder; temperature pulse; variable thermal conductivity; dual-phase-lags

Address
A.E. Abouelregal: Department of Mathematics, Faculty of Science, Mansoura University, Mansoura 35516, Egypt

A.M. Zenkour: Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia

A.M. Zenkour: Department of Mathematics, Faculty of Science, Kafrelsheikh University, Kafrelsheikh 33516, Egypt


Abstract
Observations from past strong earthquakes revealed that near-fault ground motions could lead to the failure, or even collapse of electricity transmission towers which are vital components of an overhead electric power delivery system. For assessing the performance and robustness, a high-fidelity three-dimension finite element model of a long span transmission tower-line system is established with the consideration of geometric nonlinearity and material nonlinearity. In the numerical model, the Tian-Ma-Qu material model is utilized to capture the nonlinear behaviours of structural members, and the cumulative damage D is defined as an index to identify the failure of members. Consequently, incremental dynamic analyses (IDAs) are conducted to study the collapse fragility, damage positions, collapse margin ratio (CMR) and dynamic robustness of the transmission towers by using twenty near-fault ground motions selected from PEER. Based on the bending and shear deformation of structures, the collapse mechanism of electricity transmission towers subjected to Chi-Chi earthquake is investigated. This research can serve as a reference for the performance of large span transmission tower line system subjected to near-fault ground motions.

Key Words
long span transmission tower-line system; collapse simulation; near-fault ground motion; collapse fragility; collapse mechanism

Address
Li Tian, Haiyang Pan, Ruisheng Ma and Canxing Qiu: School of Civil Engineering, Shandong University, Jinan, Shandong, 250061, China

Ruisheng Ma: Centre for Infrastructure Monitoring and Protection, School of Civil and Mechanical Engineering, Curtin University, Kent Street, Bentley, WA 6102, Australia




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